790 PROFESSOR J. STEPHENSON ON 



Arenicola a ventral groove running the whole length of the intestine ; this is probably, 

 according to the authors, the morphological equivalent of the siphon of Capitellids, but 

 they see no reason to regard it or any other part of the alimentary canal as respiratory 

 in function ; the cilia work towards the anus. Cerruti (12) has found in Microspio 

 mecznikowianus a ventral groove in the intestine, which he regards as the equivalent 

 of the accessory gut of other Annelids ; the ciliary current in the posterior portion of 

 the intestine is directed forwards, and the water thus introduced appears to serve a 

 respiratory purpose. 



(3) Respiration through the general internal surface of the intestine, hy means of 

 the introduction of water at the anus, hut ivithoat specially differentiated mechanism. 



Detailed observations on this mode of respiration in Polychseta, as in Oligochseta, 

 are almost wanting. I have, however, met with a number of isolated statements, 

 couched usually in general terms, which show that the phenomenon is generally recog- 

 nised, even though the extent of its occurrence has not yet been investigated. 



Thus QuATREFAGES (38), referring to his observations on the swallowing of air and 

 water by Syllids and Hesionids [cf ante), introduces the subject by saying : " The 

 digestive tube either in its entirety or in some portion of its extent also appears to me 

 to be able to take an active part in respiration." It is possible that he may have had 

 in mind a general activity of the intestinal wall in the manner above specified, though 

 he makes no further mention of it. 



EisiG (17, c/! supra) speaks of diffuse alimentary and cutaneous respiration as being 

 the primitive form. I have not, however, found any recognition of the fact that this 

 diffuse alimentary respiration is still widely existent in present-day forms ; and in his 

 earlier paper (16), speaking of " an animal which normally respires by means of a stream 

 of water driven through its alimentary canal," the stream is evidently conceived as 

 entering at the mouth. 



Malaquin (30), though furnishing a detailed account of the intestine of Syllids, 

 makes no mention of its respiratory function. He notes that the posterior part of the 

 intestine is more transparent than the anterior portion, and is ordinarily yellow ; the 

 epithelium here is not secretory, and is always strongly ciliated (in his fig. 35, PI. viii., 

 the cilia are shown directed posteriorly, and are presumably meant to be working 

 towards the anus). He mentions that Claparisde had previously observed refractile 

 concretions in this part of the intestinal wall, and had hence, supposing it to be 

 excretory, called it the "urinary portion" of the tract. The results of keeping the 

 animals in water containing carmine and fuchsin are given : " The only part of the 

 digestive tube to be distinctly coloured is the posterior intestine ; here are situated the 

 youngest cells, i.e. those most favourably constituted for the manifestation of osmotic 

 phenomena. The posterior intestine seems thus to be the principal seat of absorption 

 of matters elaborated by the anterior and middle portions of the tube. It also seems 

 to be an organ for the arrest of non-assimilable products ; which explains the presence 

 of the numerous urinary concretions found in the two lateral grooves of its wall." It 



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